1. Field of the Invention
The invention relates to a refractory guide tube adapted to be inserted in the wall of a metallurgical furnace.
2. Description of the Prior Art
Metallurgical furnaces of the type with which this invention is used have apertures through which the furnace interior can be inspected or samples of metal or slag can be withdrawn during an operation, or the temperature of the metal or slag can be measured (either continuously or not) and the furnace atmosphere can be measured. For example, continuous measurements can be made of the temperature of a metallurgical furnace in the manner disclosed in U.S. Pat. No. 3,786,161 and U.S. Pat. application Ser. No. 369,356 in the name of the present applicant. Rod-shaped measuring and observation devices are inserted through the apertures and can slide in refractory guide tubes provided in the thickness of the furnace wall.
The known refractory guide tubes are solid and do not usually wear at the same rate as the adjacent surface of the furnace wall in which it is inserted. When the refractory guide tube melts more slowly than the furnace wall, the end of the tube projects into the interior of the furnace and various material, more particularly scrap, may fall on it. Consequently, the measuring instruments are not protected in that end of the guide tube which projects inside the furnace.
On the other hand, if the refractory guide tube melts more quickly than the furnace wall, the end of the tube inside the furnace has a funnel-shaped opening. This results in two disadvantages. Firstly, the end of the measuring rod receives lateral radiation in the funnel, in addition to frontal radiation. Secondly, the funnel makes it more difficult to clean the end of the measuring rod. Spattered liquid metal or slag solidify on the rod and cannot be loosened, so that the rod jams during the withdrawal movement. Furthermore, the end of the rod becomes clogged, thus reducing its thermal sensitivity.
As is known, the refractory material forming the guide tube can be selected so as to have a melting temperature approximately the same as that of the furnace wall. In such cases, however, it is usually found that the guide tube tends to melt more quickly than the wall at the beginning of the operation and more slowly at the end of the operation.